1  /* Copyright (C) 1995-2023 Free Software Foundation, Inc.
       2     This file is part of the GNU C Library.
       3  
       4     The GNU C Library is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the License, or (at your option) any later version.
       8  
       9     The GNU C Library is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  #include <errno.h>
      19  #include <fcntl.h>
      20  #include <unistd.h>
      21  #include <netdb.h>
      22  #include <not-cancel.h>
      23  #include <stdbool.h>
      24  
      25  #define HOSTIDFILE "/etc/hostid"
      26  
      27  #ifdef SET_PROCEDURE
      28  int
      29  sethostid (long int id)
      30  {
      31    int fd;
      32    ssize_t written;
      33    int32_t id32 = id;
      34  
      35    /* Test for appropriate rights to set host ID.  */
      36    if (__libc_enable_secure)
      37      {
      38        __set_errno (EPERM);
      39        return -1;
      40      }
      41  
      42    /* Make sure the ID is not too large.  Needed for bi-arch support.   */
      43    if (id32 != id)
      44      {
      45        __set_errno (EOVERFLOW);
      46        return -1;
      47      }
      48  
      49    /* Open file for writing.  Everybody is allowed to read this file.  */
      50    fd = __open_nocancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
      51    if (fd < 0)
      52      return -1;
      53  
      54    written = __write_nocancel (fd, &id32, sizeof (id32));
      55  
      56    __close_nocancel_nostatus (fd);
      57  
      58    return written != sizeof (id32) ? -1 : 0;
      59  }
      60  
      61  #else
      62  # include <string.h>
      63  # include <sys/param.h>
      64  # include <resolv/netdb.h>
      65  # include <netinet/in.h>
      66  # include <scratch_buffer.h>
      67  
      68  long int
      69  gethostid (void)
      70  {
      71    char hostname[MAXHOSTNAMELEN + 1];
      72    struct hostent hostbuf, *hp;
      73    int32_t id;
      74    struct in_addr in;
      75    int herr;
      76    int fd;
      77  
      78    /* First try to get the ID from a former invocation of sethostid.  */
      79    fd = __open_nocancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
      80    if (fd >= 0)
      81      {
      82        ssize_t n = __read_nocancel (fd, &id, sizeof (id));
      83  
      84        __close_nocancel_nostatus (fd);
      85  
      86        if (n == sizeof (id))
      87  	return id;
      88      }
      89  
      90    /* Getting from the file was not successful.  An intelligent guess
      91       for a unique number of a host is its IP address.  To get the IP
      92       address we need to know the host name.  */
      93    if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
      94      /* This also fails.  Return and arbitrary value.  */
      95      return 0;
      96  
      97    /* Determine the IP address of the host name.  */
      98    struct scratch_buffer tmpbuf;
      99    scratch_buffer_init (&tmpbuf);
     100    while (true)
     101      {
     102        int ret = __gethostbyname_r (hostname, &hostbuf,
     103  				   tmpbuf.data, tmpbuf.length, &hp, &herr);
     104        if (ret == 0 && hp != NULL)
     105  	break;
     106        else
     107  	{
     108  	  /* Enlarge the buffer on ERANGE.  */
     109  	  if (ret != 0 && herr == NETDB_INTERNAL && errno == ERANGE)
     110  	    {
     111  	      if (!scratch_buffer_grow (&tmpbuf))
     112  		return 0;
     113  	    }
     114  	  /* Other errors are a failure.  Return an arbitrary value.  */
     115  	  else
     116  	    {
     117  	      scratch_buffer_free (&tmpbuf);
     118  	      return 0;
     119  	    }
     120  	}
     121      }
     122  
     123    in.s_addr = 0;
     124    memcpy (&in, hp->h_addr,
     125  	  (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
     126    scratch_buffer_free (&tmpbuf);
     127    /* For the return value to be not exactly the IP address we do some
     128       bit fiddling.  */
     129    return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);
     130  }
     131  #endif